This is a very complex matter that requires a deep discussion of not only Orthodox ecclessiology, but also the history of the Russian Orthodox Church before, during, and after the October Revolution. I will start at the very beginning. Roughly around the 1880's and 1890's, a rough split based on far earlier divisions in Russian society and the Russian Orthodox Church began to take place. One can very broadly define these earlier rifts as a conflict between progressivism and traditionalism, liberalism and conservatism, or pro-Western versus pro-Byzantinist thought. All of the definitions I have just given you are vast oversimplifications, so be careful when applying them. Only one of the two rough groups that formed actually has a name: the живоцерковцы (lit. "men of the Living Church"; they are actually more commonly known under the name of обновленцы, "renewalists"). This Living Church Movement pushed for a far more active involvement of the Church in social life while still wanting the Church to exist in the state it was in. This was in the shape of what was for all intents and purposes a ministry of the Russian Empire under the leadership of the Святейший Правительствующий Синод (Most Holy Governing Synod). The Synod was the brainchild of the tsar who is known in the West as Peter I "The Great" and totally enslaved the Church to the state in an almost caeseropapist arrangement, thereby smashing the Byzantine principle of symphonia and alienating the Church from the great mass of society. The results of this action were threefold: first, the nobility became heavily Westernised and almost totally separate from its subjects; second, Western (mainly Scholastic, but also significant Protestant) theological influences started infiltrating the Church, which was now practically a ministry and was also forced to ape the West; third, the farmers (who are often erroneously called serfs, but that is a matter for another discussion), craftsmen, and merchants lost the moral guide that was the Church and thus began sinking into alienation and depravity. What event this 'reform' laid the foundations should be quite clear. Leaving this aside, this group of proto-живоцерковцы essentially wanted the Church to become a social arm of government, a desire that breaks centuries upon centuries of Church tradition and which is warned against very heavily in the Bible. Opposing them were a loose group of what a good acquaintance called the 'group of future saints': these were traditionalists who stood for close links with the people, strong, conservative values, and a burning loyalty towards Church doctrine. One very good example of this group is Saint John of Kronstadt, a man who enjoyed true communion with the people without having to lower himself to their level. These two groups remained locked in something resembling a cold war until a crucial moment: the abdication of Tsar Nicholas II and the fall of the Russian imperial government. On 14 August 1917, the Russian Orthodox Church convened a Local Council in Moscow and elected the bishop of Moscow, Tikhon, to the post of patriarch. Tikhon took a hard anti-Communist line, allowed the Russian Orthodox Church in America to split off and continue as a separate entity. He also declared the future Russian Orthodox Church Outside Russia (ROCOR), which was then composed of several exiled bishops in Czechoslovakia, to be schismatic from Moscow's point of view. In 1923, however, Tikhon was forced to declare himself to "no longer be an enemy to the Soviet government" under great duress. This declaration was followed by his being deposed by a Soviet-backed group of живоцерковцы, a move that is at best highly suspect and at worst completely illegitimate according to Church doctrine; this group founded a High Church Administration to manage the Church, but it did not remove Tikhon from his place as patriarch (1) Tikhon later published a declaration that called all bishops to ignore the Administration and to declare it to be illegal. The actual situation soon became far more complex. Tikhon died in abominable conditions in 1925; the position of Patriarch remained open. The position was filled by a locum tenens, metropolitan Peter (Polyanskiy). Peter published a declaration declaring the 1923 removal of Tikhon to be illegal. This declaration was signed by a large group of bishops. Peter was eventually arrested, but not before leaving a declaration which gave some guidelines as to who the next locum tenens should be. This position was filled, however, not by a member of the old guard, but by a bishop called Sergius, who became locum tenens of the locum tenens. This Sergius was a живоцерковец, was backed by the Soviet government, and was ready to compromise with this government. He eventually did so in 1927 through an infamous declaration that called upon all churchmen and laymen to "show that we are not in league with the enemies of our (!!!) Soviet government... [and stand with] our Government and people...". Naturally, this clear capitulation to an openly anti-Christian government is already grounds to declare Sergius' hierarchy (which soon gained the name Sergianism) anathema, which the bishops who backed Peter quickly did. The leader of the anti-Sergianite movement coalesced around the Bishop of Leningrad, Joseph (Petrovykh), who was also named as the rightful locum tenens of the locum tenens. Thus begins the conflict between the Sergianites, backed by the Soviet government, and the Josephites. Enormously outnumbered and outgunned, the Josephites were horrifically persecuted along with thousands of priests and monks, hundreds of bishops, and hundreds of thousands of laymen, all with the de-facto approval of Sergius (2). These persecutions eventually grew so heavy that parts of the Josephites went underground to form what is known as the Catacomb Church. These groups held mass in hidden locations and abandoned churches and struggled daily for survival. Soon, another problem turned its head: in the chaos and confusion of the Great Purge and the Second World War, several groups went so deeply underground that they disappeared entirely. This creates great problems for anyone trying to recreate the old, non-Sergianite hierarchy, and many remain undiscovered to this day. One player that was mentioned earlier remains out of the picture: ROCOR. The group of bishops that formed it saw its numbers significantly bolstered by their compatriots fleeing Russia and clustered into several large communities spread around the world. The council of bishops also rejected Sergius' 1927 declaration and established their own hierarchy with a patriarch. Although the legitimacy of the ROCOR is somewhat difficult to define, it was, for all intents and purposes, a legitimate temporary structure until the mother Church could be recovered. One would think that this actually had a chance of happening, if one was not aware that the Russian Orthodox Church itself is lapsed. This fact alone should have meant that the ROCOR would be wise to never approach it. However, lured in by slogans of a "Russian religious revival" and a "new era for Orthodoxy", the ROCOR signed an Act of Canonical (!!!) Communion with the Russian Orthodox Church, effectively lapsing it and integrating the Sergianites' main opponent as far as ecclesiological legitimacy is concerned. (1): this effectively meant that it had control over 'Church policy', but did not have the legitimacy conferred by the position of the Patriarch. (2): only when reading this a second time do I realise how utterly insane it is to condone a government while that very same government is slaughtering your own clergy and flock by the thousands.